This invention relates to absorption heating and cooling systems and, in particular, to a refrigerant control apparatus for facilitating the conversion of such systems from operation in a cooling mode to operation in a heating mode.
As is well known, in an absorption heating and cooling system, a refrigerant is initially brought together with an absorbent capable of holding a high concentration of refrigerant to produce a solution suitable for use in the process. Under operating conditions that vary, the amount of refrigerant necessary to keep the system running efficiently will also vary. During operation in the cooling mode, the concentration of refrigerant is preferably relatively low, i.e., the solution is preferably relatively strong. Under this condition, the factors that limit the concentration of the refrigerant are the need to prevent cavitation from occurring in the refrigerant pump of the evaporator or crystals of absorbent from forming in the sump of the absorber. As a result, it is a common practice to equip the system with a cooling mode refrigerant adjusting system which includes a storage reservoir that is able to store enough refrigerant to prevent the solution from becoming too strong, and to store refrigerant in or release refrigerant from this reservoir as necessary to keep the concentration of the solution within acceptable limits as the demand for cooling fluctuates over the range of conditions over which the system is designed to operate. This storage reservoir often takes the form of a sump located within the system condenser. Since the range of refrigerant concentrations necessary to accommodate this range of conditions is relatively small, the storage capacity which this sump must have in order to accommodate this range of conditions is also relatively small.
One example of a cooling mode refrigerant adjusting system of the above-described type is described in unexamined Japanese application 62-178858, which is assigned to Ebara Ltd. of Tokyo, Japan. In the latter application, there is disclosed an absorption machine in which the gravity flow of liquid refrigerant between the system condenser and the system evaporator is controlled in response to certain sensed system related conditions, such as the solution temperature as it is leaving the absorber. A reservoir for liquid refrigerant is provided inside the condenser and the refrigerant is supplied to the evaporator through a first flow path under normal operating conditions. Upon the sensing of an operational condition that demands an increase in the quantity of refrigerant, a second flow path is opened which supplies additional refrigerant from the condenser sump to the evaporator.
Another example of a refrigerant adjusting system is described in copending U.S. patent application Ser. No. 09/244,910, filed Feb. 4, 1999, which is commonly assigned herewith, and which is hereby expressly incorporated by reference herein. In the latter application, there is disclosed an absorption type machine in which refrigerant is stored in a holding tank that is separate from the condenser sump and that is filled via a refrigerant bleed line. The desired refrigerant concentration is then maintained by releasing refrigerant from the holding tank under the control of a microprocessor in response to the sensing of a need for additional refrigerant.
An example of a refrigerant adjusting system that is specially adapted for use in an absorption type refrigerator is described in U.S. Pat. No. 5,806,325 (Furukawa et al). In the latter patent there is described an absorption type refrigerator in which a storage reservoir is formed in the condenser by a dam with an array of holes that allows the rate at which refrigerant is released to vary as a function of the rate at which refrigerant condenses and, consequently, as a function of the cooling load that the refrigerator must support.
During operation in the heating mode, the solution is preferably as weak as the capacity of the system permits. As a result, when an absorption heating and cooling system is switched from operation in its cooling mode to operation in its heating mode, it is desirable to introduce as much additional refrigerant into the system as is possible.
Prior to the present invention, the additional refrigerant necessary to enable the system to operate efficiently in its heating mode was provided in one of two ways. A first of these was to pump the additional refrigerant from a specially provided storage tank. This approach is not cost effective, however, not only because of the cost of providing a storage tank having a suitable capacity, but also because of the cost of providing a pump and pump control circuitry to perform a function that needs to be performed only a relatively small number of times a year.
A second way of providing the additional refrigerant necessary to enable the system to operate efficiently in its heating mode was to release into the system the contents of the refrigerant storage reservoir or tank that is used as a part of its cooling mode refrigerant adjusting system. This approach is not desirable, however, because this reservoir or tank stored only the amount of refrigerant necessary to support the ability of the system to accommodate fluctuating cooling loads. This approach is also not desirable because it may direct the refrigerant through the spray head of the evaporator, and thereby introduces into the system a restriction which serves little purpose when the system is operating in its heating mode.
In view of the foregoing, it will be seen that, prior to the present invention, there existed a need for a simple, inexpensive, and low loss way of releasing into to and removing from an absorption type heating and cooling system the refrigerant necessary to switch the system between operation in its heating and cooling modes.